1. Field of the Invention
The present disclosure relates to the art of work holders and, more particularly, to clamps for holding objects such as cylindrical components, such as tubes.
2. Description of the Related Art
Orbital welding devices, tube welders, or weld heads are well known in industry and are used to fuse together two cylindrical or tubular components. Tube-to-tube welding or tube welding requires that two tubing sections be held so that they are in coaxial abutment during the orbiting of the weld head or its electrode about the seam of the two tubes. A tube or cylindrical component could be a bare piece of tubing or a tube that extends from a component such as a valve, mass flow controller, or the like. Tube welding devices usually require clamps for holding the pieces of tubing in position for being welded to each other. Arc Machines Inc., the assignee of this application and the invention described in the application, makes a well-known line of tube welders such as the Model 8 or 9 series. The clamp can be a separate mechanism or integrated within the structure of the welding device.
Clamps must open to receive the cylindrical component and then clamp onto the cylindrical component, firmly holding it in place relative to the weld head. However, due to the permissible variation in the outer diameter of the tubes, tightly clamping the tubes without causing undue damage to the tube can be problematic. For instance, a two inch diameter tube may have a minimum permissible diameter of 1.985 inches and a maximum permissible diameter of 2.025 inches, a range of 0.040 inches. Existing tube clamps are lacking in their ability to tightly and consistently clamp the tubing over its entire permissible range of outer diameters, without causing excessive damage to the tube, such as deforming the tube or scarring it.
U.S. Pat. No. 4,810,848 to Kazlauskas, the disclosure of which is incorporated by reference for all purposes allowed by law and regulation, discloses a tube welder having a pair of identical arc-shaped or collet shaped first clamping plates. The clamping plates each have a centrally located, half circle indentation which cooperate together to form part of a through opening. The clamping plates can fasten to the tube sections in order to hold the tube sections in coaxial abutment.
Slots forming cantilevers are cut about the half circle indentations to permit a limited amount of expansion to accommodate the standard variation of the tube outer diameters. While clamping plates with a basic cantilever design may be made to accommodate a range of variance in tube diameter, the firmness of the clamping is poor at certain diameters, such as a minimum diameter, and therefore undesirable. Additionally, after the point of maximum deformation of the cantilevers, where the slot width is generally near zero, the clamping force exerted on the tube will no longer be elastic and the possibility of damage to the tube will exist if further clamping pressure is applied.
U.S. Pat. No. 4,973,823 to Benway et al. discloses collets for clamping devices for cylindrical workpieces that have individual surface portions in the form of clamp faces formed by a concentric slot and a radial slot. These individual surface portions have the form of cantilever beams. The individual surface portions are thus mounted for independent flexing movement to accommodate workpiece tolerance variations. Again, this basic cantilever design is limited in its clamping range.
The clamping plates or collets of the references discussed above all rely only on cantilever action to provide pressure against the workpiece. Clamping plates and collets using cantilever action will have a large degree of clamping force variation even within the normal production tolerances of a given tube diameter. Additionally, once the moveable element has rotated radially a certain distance, it will contact the opposing wall of the related slot and stop providing elastic pressure to the workpiece. Simply providing a wider slot to accommodate greater displacements can either over stress the material causing strain, or will not perform well at one extreme of the tube's permissible diameter variance. The result is ineffective clamping unless greater compression is provided. Greater compression may damage either the cylindrical workpiece or the clamping plate because the compression is materially limited. Thus the range of sizes that may be accommodated while providing adequate clamping pressure is limited.
Accordingly, there has been a long-felt need in the art for a clamp that permits the firm clamping of a cylindrical component at substantially all possible deviations from the nominal value of the diameter so that rotation and/or twisting both radially or axially of the workpiece is minimized. What is also needed is a clamp that minimizes the deformation of the cylindrical component. Additionally, what is needed is a clamp with the ability to provide substantially consistent clamping force over a wide range of tube diameters.